private double getBackgroundExpire(String command){
    command = command.replaceAll("y", "*31536000000+");
    command = command.replaceAll("mo", "*2628000000+");
    command = command.replaceAll("w", "*604800000+");
    command = command.replaceAll("d", "*86400000+");
    command = command.replaceAll("h", "*3600000+");
    command = command.replaceAll("m", "*60000+");
    command = command.replaceAll("s", "*1000+");
    command = command.substring(0, command.length()-1);
    Double ret = 0.0;
    ret = new Expression(command).resolve();
    //System.out.println(ret/1000);
    return ret;
}